This invention relates to an improved method and apparatus for separating particles from gases by use of centrifugal separators. It is particularly useful for separating particles of catalyst from hydrocarbon vapors issuing from a catalytic cracking process and can also be advantageously utilized in other applications such as for removing suspended solids from gases fed to boilers, resulting from coal gasification and liquefaction, molecular separation; and for use with supercharged boilers.
In a catalytic cracking process, particle separators embodying the present invention are especially useful in "third stage" separation, that is, in separation of relatively smaller particles from gas after the relatively larger particles have already been removed by cyclone separators. Third stage separation is quite important for air pollution control purposes and for economizing. Some active catalyst can advantageously be recovered and re-used by this mode of separation. Furthermore, purified clean gas from this third stage separation can be used to drive a turbine without any significant erosion of the turbine blades which would otherwise be caused if such particles were still present in the gas being fed to the turbine.
Centrifugal separators of the type having an outer tube and a concentric inner tube defining an annular passageway therebetween are known to the art. In U.S. Pat. No. 3,443,368, of which I am a co-inventor, a centrifugal separator of the above type is described. The inner tube, which also acts as a clean gas discharge line, has an open-mouthed end extending into the region defined within the outer tube. The inner surface of the outer tube is lined with refractory ceramic.
In operation, gas laden with particulate matter enters the annular passageway in a swirling motion generated by swirl vanes associated with the separator. Centrifugal force throws the particulate matter in the gases outwardly against the inner surface of the outer tube. These particles, along with some bleed gas, enter a narrow annular trough at the bottom of the separator and are discharged therefrom. The clean gas, now in a purified state, flows up into the open mouth lower end of the inner (clean gas discharge) tube and ascends upwardly, exiting the separator at the top.
In my U.S. Pat. No. 3,631,657, an apparatus for cleaning gas comprising an inner vessel enclosed within an outer vessel is disclosed. The inner vessel is partitioned into a clean gas chamber, an intermediate inlet chamber and a particle collection chamber. Gas to be purified is fed into the intermediate inlet chamber, which contains a plurality of centrifugal separators, as for example, those shown in the above-mentioned U.S. Pat. No. 3,443,368.
The bottoms of the separators communicate with the particle collection chamber to deposit the separated particles therein. The inner clean gas discharge tube of the several separators direct the clean gas upwardly into the clean gas discharge chamber. The purified gas flows through holes in the sidewall of this chamber, into the space defined between the inner and outer vessel, and is discharged from the apparatus through an outlet nozzle associated with the outer vessel.
U.S. Pat. No. 2,941,621 shows another embodiment of a known centrifugal separator including an outer tube and an inner clean gas discharge tube positioned concentrically therein. Gas to be purified enters an annular channel defined between the inner and outer tubes with a swirling motion imparted by swirl vanes. The separated particles and bleed gases flow down to the bottom of the outer tube and are discharged therefrom while the purified clean gas ascends through the inner discharge tube and exits the separator from above. A similar separator is also disclosed in U.S. Pat. No. 3,006,854.
A plurality of such separators are included within a single vessel partitioned into a center inlet chamber which supports the separators and communicates with the incoming gas to be purified, a lower collecting chamber in communication with the bottom of the separators for receiving discharged particles and bleed gas, and an upper clean gas outlet chamber in communication with the inner discharge tube for receiving purified gas. Duct means are provided for bypassing the upper clean gas discharge chamber and introducing the gas to be purified directly into the central separation chamber.
The prior art centrifugal separators also experienced erosion problems caused by the recycling of the separated particles. That is, even after particles were separated from the gas, these particles were still trapped within the separators and subjected to turbulent forces causing them forcefully to impact against and continue to churn against the walls of the separator, resulting in severe erosion.
Also, because the purified gas exits from the top of the separator while the separated particles and bleed gas exit from the bottom of the separator, the disclosed prior art separator vessel, must, by necessity, position the clean gas discharge chamber above the separators, and position the collecting chamber below the separators. Thus, the chamber in which the separators are housed must be positioned between the upper and lower chambers thereby requiring the complex arrangement of a separate air inlet duct means to transport the particle-laden gas through the upper clean gas discharge chamber for introduction into the separation chamber of the vessel.
It is an object of the present invention to provide an improved separator, separator vessel and method of separation overcoming the disadvantages of the known prior art. Specifically, the present invention provides a simplified, economical and durable separator and separator vessel which is highly efficient and easy to maintain. Moreover, a novel method of separating particles from gases is provided.